Verify Stokes theorem for $F=(x^2-y^2){\bf i}+2xy{\bf j}$ in a rectangular region

Question

Verify Stokes theorem for $F=(x^2-y^2){\bf i}+2xy{\bf j}$ in the rectangular region in the $xy$ plane bounded by the lines $x=0,x=a,y=0$ and $y=b$.